Pressure responsive device



Filed April 5, 1947 Patented Sept; 1951 UNITED STATES PATENT OFFICEPRESSURE RESPONSIVE DEVICE George Forrest Drake, Rockford, Ill.,assignor to Woodward Governor Company, Rockford, 111.,

a corporation of Illinois Application April 3, 1947, Serial No. 739,052

above character in which the different pressures acting on the parts ofthe seal are completely balanced whereby to permit extremely small forcechanges to be transmitted mechanically from one space to the other.

A more detailed object isto transmit the control force from one space tothe other through a flexible diaphragm wall on which all forces due tothe pressure differences between the spaces are completely balanced.

Other objects and advantages of the invention will become apparent fromthe following detailed description taken in connection with theaccompanying drawing which is a longitudinal crosssectional view of areciprocating type of fluid seal embodying the novel features of theinvention.

For purposes of illustration, the drawing shows the improved seal as ameans for enabling a control motion derived in a space 6 which is at onepressure to be transmitted mechanically to another space 30 at adifierent pressure and, in the latter space, applied to the movableelement l 01' a control device such as a valve 2 shown as a land on astem 4 coacting with a port 5 in a surrounding bore.

In this instance, the control motion is produced by pressurefluctuations transmitted to the chamber 6 through a passage 3 so thatthe illustrated assembly constitutes a pressure responsive relay. Itwill be understood, however, that this is only one oi many possible usesfor the improved seal.

The chamber 6 is defined by rigid walls I one 01' which has a circularopening 8 therein closed by an axially flexible diaphragm '9 clampedaround its periphery against the defining wall of the opening. Axiallyspaced from the diaphragm 9 is a second similar diaphragm iii of thesame effective pressure area clamped against the end of a casing H whichis supported by or otherwise flxed with respect to the casing 'l as by arigid connection l2.

The centers of the axially spaced diaphragmsare rigidly connected by astem l3 which projects through the diaphragm 9 and into the chamber. 8and is exposed between the diaphragms for connection to the controlelement l. Thus, the chamber is sealed effectually against fluid leakagetherefrom but mechanical motion may be chambers.

transmitted therefro to the exterior space by axial flexing of thediaphragm, the scale of which does not vary the transmitted forceappreciably for short motions.

Means is provided for balancing the pressure acting on the twodiaphragms 9 and I0. For this purpose, the casing ll supporting thediaphragm Ill defines a chamber 20 enclosing the outer side of thediaphragm and communicating with the chamber 6 through a passage 24.Herein, the latter extends lengthwise through the stem [3 and opens atopposite ends within the respective Since the diaphragms are exposed onadjacent sides to the space 30 and on remote sides to the chambers 6 and20 which are at equal pressures, the pressure forces acting on theequally sized diaphragms will be balanced. All diii'erential areas andrubbing friction are eliminated and the connecting member' l3 willrespond to very small changes in a control force applied to the latterat a point within the chamber 6.

While the control force may be derived from various sources, it isproduced in the illustrated embodiment by pressure fluctuations in thepipe 3 which leads to the chamber 8. To measure these fluctuations, apressure responsive device in the form of a closed evacuated bellows I5is mounted within the chamber 8 with one end wall ll connected rigidlyto the inner end of the stem It. The end walls of the bellows areseparated and urged apart by a spring l6 and the other wall I1 issupported for axial movement so that the control point 01' the relay asa whole may be adjusted. This is accomplished herein by connecting thewall ll to the end of a rod l8 which projects through and is guided atiii in one wall of the chamber 8 in axial alinement with the stem 13.Any suitable means such as a screw 25 may be employed to adjust the rodl8 to different positions to thereby change theposition of the normallyfixed wall I! of the bellows.

Externally of the chamber 6 and of the chamber 20 is a mechanicalconnection extending to the control element I to transmit to the latterthe reciprocatory motion of the stem I3. Herein, this connectionincludes a rigid yoke 2| fixed at 22 to the stem ES connected at theother end to the valve stem 4, the connection being through a spring 23in the present instance.

For any given setting of the adjusting rod l8, it will be apparent thatthe valve element I will occupy a position corresponding precisely tothe pressure prevailing in the chambers 8 and 20. Now, if the controlpressure increases, the bellows IE will collapse correspondingly,thereby moving the stem l3 and the valve element I upwardly. Conversely,in response to a drop in the control pressure, the bellows will expandaxially thereby moving the valve element I downwardly. I

I claim as my invention:

1. The combination of means defining a closed fluid chamber having onewall including an annular axially flexible diaphragm, said chamber beingsubjected to a variable pressure different from the pressure in thespace surrounding the chamber a second diaphragm of the same efi'ectivearea axially spaced from said first diaphragm and forming one wall of aclosed chamber disposed on the side of the diaphragm opposite said firstchamber, a stem rigidly connecting the centers of said diaphragms andprojecting into said first chamber, means within one of said chambersfor applying a control force to said stem variable in accordance withpressure changes in said variable pressure chamber, means establishingcontinuous communication between said chambers to equalize the pressurestherein, and means connected to said stem externally of said chambersand adapted for connection with a device to be operated.

2. The combination of, means defining a closed fluid chamber subjectedto a variable pressure different from that of the surrounding space andhaving a wall including an axially flexible diaphragm, a seconddiaphragm of the same effective area axially spaced from the firstdiaphragm and forming one wall of a second closed chamber disposed onthe side of said second diaphragm remote from said first chamber, amember rigidly connecting said diapbragms, means establishing continuouscommunication between said chambers to equalize the pressures therein,means within one of said chambers for applying a control force to shiftsaid member axially and varying in accordance with the pressure changesin said first chamber, and means disposed externally of said chambersfor transmitting the axial movements of said diaphragms.

3. The combination or means defining a closed fluid chamber having onewall including a flexible diaphragm, the fluid pressures inside andoutside 01 said chamber difl'ering from and varying relative to eachother, a second closed chamber having one wall closed by a flexiblediaphragm or the same effective area as said first diaphragm, meansestablishing continuous communication between said chambers to equalizethe fluid pressures therein, a device responsive to deviations of thepressure within the said first chamber relative to a predeterminedpressure value and to apply to said diaphragm a force corresponding inmagnitude and direction to such deviation, and means externally of saidchambers rigidly connecting said diaphragms for flexure in unison.

4. A pressure balanced seal comprising two flexible diaphragms of equaleffective areas, means rigidly connectin said diaphragms i'or flexingthereof in unison, and interconnected chambers defined in part by therespective diaphragms, the fluid pressures inside and outside of saidchambers differing from and varying relative to each other, a devicewithin one 01 said chambers for moving the diaphragm of such chamber inaccordance with pressure changes within the chamber, the pressures insaid chambers acting on said diaphragms to balance each other.

GEORGE FORREST DRAKE.

REFERENCES crrEn The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,042,523 Graham June 2, 19362,338,505 Gregg Jan. 4, 1944 2,365,650 Shaw Dec. 19, 1944 2,477,233Bristol July 26, 1949

